Catalytic reforming of hydrocarbons



Patented 17, 1948 CATALYTIC REFORIVIING F HYDROCARBONS Kenneth K. Kearby, Cranford, N. J., asslgnor to Standard Oil Development Company, a corporation of Delaware.

No Drawing. Application March 2. 1948,

I serial No. 12,681

The present invention relates to improvements 2 in the catalytic treatment of hydrocarbons, and,

more particularly, it relates to improvements in the use of catalysts for reforming naphthas and/or aromatizing aliphatic hydrocarbons.

This application is a continuation-in-part of copending applicationSerial No. 611,907, filed August 21, 1945, now abandoned.

It is known that petroleum naphthas and similar hydrocarbon mixtures containing appreciable quantities of naphthenes can be subjected to a so-called reforming operation to yield a liquid product of improved octane number boiling in the gasoline range.

Depending on reaction conditions, catalytic reforming operations are generally referred to as either hydroforming or aromatization reactions.

By hydroforming is ordinarily meant an operation conducted at elevated temperatures and pressures in the presence of a solid catalyst and added hydrogen, wherein a hydrocarbon fraction is increased in aromaticity and wherein there is no net consumption of hydrogen. The term "aromatization refers to an operation in which a hydrocarbon fraction is treated at elevated temperatures, but at substantially atmospheric pressure, in the presence of a solid catalyst, for the purpose of increasing the aromaticity of the hydrocarbon fraction.

Catalytic reforming operations are usually carried out at temperatures of around 900-1000 F. in the presence of such catalysts as molybdenum oxide, chromium oxide, nickel sulfide, or tungsten sulfide, or any of a number of oxides or sulfides of metals of groups IV, V, VI, VII and VIII of the periodic system. These catalysts are usually supported on a base or spacing agent and the most commonly used base is alumina, either of the gel type or precipitated alumina. For example, a modified alumina, made by heat treating hydrated aluminum oxide, has been used as a support or extending agent for the active reforming catalysts mentioned above. Thus, a good catalyst for reforming or hydroforming is one containing about molybdenum oxide supported on an alumina base. However, alumina, in its various forms is not heat-stable, particularly at regeneration temperatures which are of the order of 1000-1200 F. At temperatures in the neighborhood of 1100 F. or higher, alumina is definitely impaired by prolonged heating, and this impairment is reflected in the loss of activity of the catalyst composition of which the alumina is the support or spacing agent. Consequently, since the aromatizatlon of a paraffin, such as, for ex- 16 Claims. (01. 260-6735) ample, normal heptane to form toluene, is an operation which requires high temperatures, the ordinary alumina base does not withstand the temperatures necessary for this particularconversion for a prolonged period of time.

A method has now been found for treating alumina to increase its heat resistance so that it may act more efliciently as a support for reformmg and aromatization reactions and for similar high temperature catalytic processes, and will have a high degree of activity under the most severe temperature conditions for an extended period of time. base or support is prepared by combining aluminum oxide with zinc oxide, preferably in molecular proportions, thereby forming zinc aluminate. This combination forms a true compound of the spinel type andis not merely a mechanical mixture, for examination of the lattice spacing in accordance with the well known procedure of X-ray diffraction proves that the combination is a true chemical compound.

It has now been found not only that zinc aluminate spinel is more heat stable than ordinary alumina but also that molybdenum oxide and chromium oxide are much more active catalysts when supported on zinc aluminate spinel than when supported on alumina.

The new catalysts of this invention are particularly suitable for use in the aromatization of aliphatic hydrocarbons at high temperatures and are also superior to those formerly used in reforming or hydroforming operations.

The main object of the present invention is to provide a heat-stable base or spacing agent for active reforming and aromatizing catalysts and particularly for oxide'sof molybdenum and chromium. Another-object of the invention is to provide a more active dehydrogenation catalyst especially for aromatizing or hydroformin'g naphthas, particularly from the standpoint of yields of aromatics in the reformed product.

A more specific object of the invention is to provide an improved catalytic process for the reforming of hydrocarbons, employing a heat-stable catalyst capable of being used at high temperatures. Other and further objects of the invention will appear from the following more detailed description and claims.

Briefly, the present invention is concerned with the improvement of hydrocarbons by contacting them under suitable conditions with a catalyst composition heretofore unknown. More particularly it is concerned with the conversion of naphthenic and paraffinic hydrocarbons to aromatic In this invention the catalyst 3 hydrocarbons by contacting them with a superior reforming catalyst. This new catalyst composition comprises a major proportion of a zinc alu- 30% of chromium oxide or of molybdenum oxide or of mixtures of these oxides. Compositions containing from 10% to 20% of molybdenum oxide or of chromium oxide or of mixtures of these oxides supported on zinc aluminate spinel are particularly effective.

These new catalyst compositions are claimed in copending application Serial No. 782,029, filed October 24, 1947, now Patent 2,447,017. Methods for their preparation .are claimed in copending application Serial No. 795,139, filed December 31, 1947.

The preferred method of preparing the new catalyst compositions of the present invention is about as follows: An acidic solution of a zinc salt such as zinc nitrate or zinc sulfate is allowed to react with a basic solution of an alkali metal aluminate such as-sodium aluminate. Zinc aluminate precipitate is separated from the resulting slurry and is washed with water, dried and then calcined at about 1000-1200 F. Molybdenum oxide or chromium oxide is incorporated into the zinc aluminate precipitate either before or after the drying and calcining treatment. A convenient method for doing this is to impregnate the precipitate with a solution of a salt of the desired metal and then convert the salt to the hydroxide or oxide by adding a base such as ammonium hydroxide.

Methods for preparing the new catalyst compositions and experimental results obtained when using these catalysts in aromatization and hydroforming operations are set forth below:

Exmul Solution A.N-ine hundred seventy-four grams of C. P. zinc nitrate, Zn(N:) 1.83:0. was dissolved in a solution of 179 cc. concentrated nitric acid in 2 liters of distilled water-and made up toa volume of 3290 cc.

Solution B.Eighty grams of pure NaOI-I was dissolved in 4 liters of distilled water and into this solution 800 grams of sodium aluminate was stirred rapidly. After stirring for two minutes, 500 cc. of a diatomaceous earth filter aid was added. Stirring was continued for one-half minute and the suspension was filtered on a Bilchner funnel, 3290 cc. of the filtrate being used for solution B. The resulting solution had a concentration of 101 grams A120: and 87 grams NazO per liter. On this basis, the acidity of the zinc nitrate (solution A) was adjusted to exactly neutralize the alkaliofthe alumina solution.

Solutions A and .B were added at equal rates over a period of'30 minutes to liters of distilled water while stirring. Stirring was continued for '15 minutes after all of A and 18 had been added and the precipitate filtered. The precipitate was washed with 6 liters of water, restirred in 12 liters of water, filtered and washed with 6 liters of water. The precipitate was dried and calcined 3 hours at, 1000 F.

The nine aluminate was mixed for 3 hours in the ball mill with a solution of 81.8 grams of C. P. ammonium molybdate dissolved in a mixture of 44 cc. concentrated ammonium hydroxide in 440 cc. of water. (Additional water was added. sumcient to form a thick paste before mixing.) The mixture was dried, pilled and calcined for 3 hours at 1000 F.

Exam: 2

4 Another catalyst was prepared as above except that the washed zinc aluminate precipitate was not dried and calcined before mixing with the ammonium molybdate solution.

Exams: 3

Aluminum hydroxide was prepared by adding 1645 cc. of a solution, identical with solution B in Example 1, to 8 liters distilled water and then adding a solution of 295 cc. concentrated nitric acid in 4 liters of distilled water. The precipitate was filtered and washed with 5 liters of distilled water.

Four hundred nine grams of fused zinc nitrate (32.5% ZnO) was dissolved in 5 liters of water and neutralized by stirring in a solution of 135 g.

of sodium hydroxide in 1 liter of water. The precipitate was filtered, washed with 3 liters of distilled water and mixed with 4 liters of distilled water. The filtrate was not clear and was used to resuspend and mix the zinc hydroxide and aluminum hydroxide precipitates. The mixture was filtered and washed on the filter with 3 liters of water. It was mixed for 3 hours in the ball mill, dried and calcined for 3 hours at 1000' F.

The product was impregnated with ammonium molybdate (40.9 g.) and finished as in Example 1. The catalyst supports prepared according to the foregoing procedures are true compounds having the formula ZnOAhOa. This has been established by comparison of the X-ray diffraction pattern of the catalyst base with published patterns for zinc aluminate. The comparison is tabulated 4 below:

Lattice spacings m Angstrom 1mm Standard Literature Values Measured on Present Catalyst Base Gamma ZnAhOs Z A1 to 1 Weak lines.

I Mailer lines for alumina.

Bee d. 6: Eng. Chem, Anal. Ed., Al o; from card file of Amer. Soc. Davey, Chairman, Pennsylvania State College.

10, 510, 511 (1938); and Gamma for Testing Materials, W. P.

It will be noted that the catalyst support prepared as set forth in the left-hand column compares very favorably with the literature data given for the compounds ZnAl-z04. In columns 3 and 4 are set forth, respectively, the data given in the literature for zinc oxide and aluminum oxide, and it is clear from these data that the new cat alyst support is not a mere mechanical mixture of these two substances, since such a mixture would give superposed patterns of ZnO and A1203. For example, in the aluminum oxide column there are no lines whatever corresponding to the 2.86 or 2.45 angstrom spacings of the sample, and under the zinc oxide column given in the foregoing table there are blanks corresponding to the 2.02 and 1.652 lines or the sample, and in this same connection at the corresponding points in columns 3 and 4 under zinc oxide and aluminum oxide. the lines dlfler beyond experimental limits of error (0.02 angstrom unit) from those determined by mm test of the new catalyst base. Hence the com- 5 pound comprising the base of this new catalyst A Y B 0 cannot be a mere mechanical mixture 04 zinc ox.- ide and aluminum oxide, but is an entirely difler- 90% zniiiioi, 11% (i c, M00. ent crystalline compound. v v 10% Alumina na Reforming or aromatizaticn processes con- 10 ducted in accordance with the present invention 7 ggg fffffffi: 'f 70 71 n may be carried out with either a fixed bed of cat- Aromaticlty, Vol. 115.. s1 is so alyst or by the use of what is known as the f fi ffifi fzfff lf 34 24 fluidized solids technique. When employing a fixed bed of catalyst, the hydrocarbon vapors are 15 I forced through the bed of catalyst in a suitable Wm betnotei from if, m z g reactor for a certain period of time, say 1 to 4 6 new gave a Wlume no Y1 of aromatics (mostly toluene) whereas alumina gave arm which time the feed is cut and with chromium oxide 349' and with mol bdenuin generating gases are passed through the catalyst on d e 24% aromatics y bed to revivify the catalyst and to remove therefrom carbonaceous or other harmful deposits Exliuru 5 l h g g ig gg'g ffgfi g jgi f $32,25 2 {$22 When testing the suitability of the catalyst of is again conducted through the catalyst bed. A gi gfig igg g a gi g ga m fig gggg fg g 331353.223; iiifiiitttfittttti si i: are

scr e aove. us,usnganap enc ee as; a weredmtde ca a ys s n ee an a um na-suppor ed ca a-. through the bed of catalyst at such a rate that the lysts in two, operating in all five 11 at a feed goglifn n fifg in a l t s f a vi g I 39 raitiea'1 oft1.2 volumes of liguid feetd per voiggae 2i 0 g c is W 0 pro P o 0 ca ys per our, at a empera ure of can be made for circulating the catalyst back and and atmospheric pressure (one hour reaction forth between a reactor and a separate regeneraperiods). The following results were obtained:

Catalyst, Parts by Wt.

oo,zmi1o,90 zii1o, 1 ,0 0 MO 85%Z11A110t. i o% Mcbi i'flttbnbi oiizlui riin a i zilun in a 2 85 Liquid Recovery, Vol. percent v 77 6 81 86 75. 5 Aromaticity, Vol. percent 71 60. 2 51 42 77. 2 Total Aromatic Yield, Vol. percent 65 48. 6 41 36 5s, 3 Coke, Wt. percent 6. 6 4. 6 v4. 6 4. 6 6. 3

tor. Such processes are now well described in the It will be noted that here, also, there is a distinct increase in the aromaticity of the product In the processes of the present invention, reacwhich is a highly desired result in reforming tion temperatures of about 800 to about 1100 F. naphthas because the aromatics improve the and preferably of about 900 to 1000 F. are suitoctane rating of the gasoline. Hence the gasoably employed and the hydrocarbon vapors are line produced by the new catalyst of this invenconducted through the catalyst at feed rate of tion would be superior to that obtained by the from 0-2 to about 1.5 liquid volumes of feed per coizventional process using a conventional catavolume of catalyst per hour. Pressures may be lys atmospheric or may be as high as 300 lbs. per EXAMPLE 6 in. When hydroforming operations are carri out, hydrogen may b add at about the rate of In other runs it was found that by decreasing 1000 to 4000 cu ft per barrel of feed Suitable the naphtha feed rate from 1.2 volumes to 0.45 volume ofnaphtha per volume of catalyst per means are provided in either the fixed bed or hour, but otherwise operating under the same fluidized bed type of operation for separating and dm 1 t f 1000 recovering reaction products con ons, name y, at a tempera ure 0 F. and under atmospheric pressure, the aromaticity EXAMPLE 4 of the product was increased from 71 to 85%. By lowering the temperature to 950 F. even better t To g ig gi' fiifi g g gg 1 2:32 results were obtained at lower feed rates, namely, 0 aroma Se at 0.25 volume of liquid naphtha per volume of all conducted at 1000 F., vaporized normal hepcatalyst per hour. At a feed rate of 0.25 volume me being Passed through at fixed bed of catalyst of naphtha per volume of catalyst per hour a. 69% at a feed rate of 1.2 volumes of liquid heptane per hqmsi yield having an aromaticity f 95% was volume of dials/13111133333 ,zit g ig fgfig 70 obtained. This represents a gross aromatic y eld Pressure- P 5 0 e of 66 volume per cent on feed. base, that is, zinc aluminate spinel, was used, and 1 p rts ygiiigilllt of i3) run B chromiugi 'rm gees 51 tllale lglowsngRiifipection: gravity 1A 1: 1. 5 5 1; oxide on al was use e amount of Cr: 3- Perm l 6 W pressure= l. .2; n l I] being 11% by weight of the mixture; and in run zfi c2 2te fiifiii it voiffiefiffi tifitteiesiit?af "0 a catalyst consisting of about 10% by weight cent P=4l.5; boiling range=200-270 r,

Influence of Iced rate and temperature on the aromatizatton o! naphtha 1 over 90% zinc alumtnate-10% molybdenum oxide catalyst 8 supported on zinc aluminate. Duration of each run was one'hour. It will be seen that ingeneral coke formation is reduced as the pressure is increased and aromatic yields are improved as the pressure is reduced.

v. v. rr

flect of pressure in hydro/arming using zinc 1m illuminate-molybdenum oxide catalyst WNFEJEIIII 3 "2 :3 3 *3 2 igpir it e 'tifffifif':::::::::::::: 2. 922 tfi y Rm 7 re 1. v. Hydrogen ma, cu. n. bl;...- 1m 1m m1 1m Aromatic! 701. Percent. 95 61 74 85 53 71 q y- V01 percent. NJ 77.2 77.9 Ill Aromattic ield, Vol. Per 66 51 57 57 46 55 6251 21: czg vgt x gentnn 6; eg 00: l: 0. w, P... Q... on 72 H 58 m u H 0.1.3.... ...a......'::::::::::::::::::::::: til rt 2:. u

l Feedo gontains 11% aromatics; naphtha same as described in Exmru'i Other runs were conducted to test the value of the new catalyst in hydroforming. In these runs an East Texas naphthenic naphtha (described in Example 5) was treated under conditions set forth below, in one case using the catalyst of the present invention and in the other run using a conventional hydroforming catalyst consisting of alumina supporting molybdenum oxide, the latter being one of the best hydroforming catalysts heretofore developed. It will be observed from thedata presented below that the use of the zinc aluminate-molybdenum oxide catalyst gave superior results, for it will be noted that the aromaticity, the grOSS yield, and the conversions were much higher in the case of the zinc spinel supported catalyst than in the case of the conventional hydroforming catalyst. These data, together with operating conditions, are set forth below:

The following runs show that when aromatizing naphtha at atmospheric pressure, dilution of the feed with hydr gen has a marked effect in reducing coke formation and also results in a llilh ly higher yield of aromatics at a given liquid recovery. Thus,,at 950 F. and 0.25 v./v./hr., dilution of the vaporized feed with two volumes oi hydrogen (2 volumes hydrogen S. T. P. per calculated volume S. T. P. of feed) decreases coke formation from 7.2% to 3.7%. and results in an increase in liquid recovery from 69% to 72%, at about 95% aromaticity. A further reduction in coke formation to 2.5 wt. per cent on feed is obtained by increasing the hydrogen dilution ratio to 4/1. A similar trend is observed at 1000 I". and 1.2 v./v./hr.

These data are summarized in the following table:

Influence of hydrogen dilution on the aromatization of naphtha 1 over 90% zinc aluminate- 10% molybdenum oxide catalyst 331232293X:::::'"::::: 0 22 1? [4-hourperiods; 1.27v./v./hr ieed rate: min 0. FJB oiHezcolbs. mdnutiofimmnlnn; '5 2/1 2/1 "0i P9 LiquidReoovery,voLPerCent..- 60 72 72 76 82 76 iromaitticitsyi yialkggr C)lent.1...1. 05 94 95 60 02 65 01118 0 8 55 V0 6! Catalyst Cen en as so 52 s1 40 Coke,wt. Per Centonleed 7.2 3.7 2.6 5.3 2.4 2.2 M00: (10%) 1 Same naphtha as described in Example 5. a 0 I Since the gaseous reaction products are largely hydrogen, it would appear that recycle of a por- O 965 956 tion of the make gas would be an eifective way Li uid Recovery, Vol. Per Cent 83.4 85. 5 g e t g a 3 g to reduce carbon formation 0 er en Aromaticity v01. Per Cent... 59 so Exsuru: 10 a r 'tssessa-te s rossrome 6,0.91' 911-. Conversion, v01. Per Cent e5 44 Further runs were made to test the suitability of the new catalyst compositions in reforming 1 Cubic feet per barrel. I Fraction oi non-aromatic portion of iced which reacts.

naphtha at various temperatures and feed rates and these data are summarized below:

Catalytic aromatization of naphtha over 90% zinc aluminate-10%molybdenum oxide catalyst Temperature F 950 950 950 950 950 1000 1000 1M0 1M 1M 10) Feed rate, v./v./hr 0.48 0. 45 1.2 0.45 0.25 0. 26 0.25 0.25 0. 48 1. 2 l. 2 1.2 1.2 1.2 Cycle 16118311, hr! 3 3 1 3 3 6 3 3 3 1 1 1 1 1 dilution ratio 0 2. 1 0 (l 2. 0 0 0 4. 2 0 0 0 0 1. 8 4. 2 Liquid recovery vol. per cent 84.4 81. 5 84.3 77.3 82.0 73. 2 68.8 72.4 67 7 76.0 77. 5 80.3 82.3 70.3 Aromaticlty, V01. per cent 61 61 55 74 73 93 95 95 85 69 61 68 62 65 Aromatic yield, vol. per cent 51 49 45 67 68 66 00 57 62 47 51 40 Coke, Wt. per cent on ieed 4. 3 2. 0 4. 6 5. 8 3. 3 5.9 7. 2 2. 6 10.9 5. 3 7. 2 6. 7 2. 4 2. 2 Gas, Wt. per cent on feed.... 6. 8 9. 8 6. 6 10. 6 7. 0 11. 4 14. 0 15.0 13. 3 12. 5 8. 9 7. 8 9. 6 13. 2 Catalyst age, cycles I 9 11 6 7 10 3 1 3 2 0 4 8 5 4 Run N n 176 179 176 176 179 184 188 188 184 184 164 176 164 188 l Nsphths same as used in Example 5.

l A cycle is a period on-streem and a period of regeneration with a mixture of air and inert gas (usually 2 hours).

Exams: 8 The etfect of pressure in hydroforming is shown by the following data. In each case the feed was a 200-270 1". naphtha of the type used in Exampie 5 and the catalyst was 10% molybdenum oxide The processes of the present invention may also be adapted to the conversion of heavy virgin naphthas containing naphthenic hydrocarbons to produce aviation safety fuels having unexpectedly high aromaticity. Thus for example. a vaporized 9 heavy naphtha may be admixed with an added gas containing free hydrogen and contacted with a catalyst of the present invention at temperatures of 900 to 1000 F. and at atmospheric pressure or at pressures as high as 200 lbs. per sq. in..

employing a feed rate of from 0.2 to 1.5 v./v./hr.,

to give high flash point, highly aromatic fuels.

Exmru 11 The following inspection data were procured with fractions of the reaction product obtained when reforming a. heavy East Texas virgin naphtha (boiling in the range of 250 to 400 F.) in the presence of a catalyst consisting of about 90% zinc aluminate and about 10% molybdenum oxide. The reaction conditions employed were: 950 F. reaction temperature, 0.5 v./v./hr. feed rate, one hour reaction periods, 40 lbs. per sq. in. absolute pressure, 1900 cubic feet of added hydrogen per barrel of naphtha.

1 These samples contained 4.0 cc. T. E. LJgal.

It will be noted from the above data that a high quality safety fuel was obtained in about 25% yield. This fuel had a boiling range of 300 to 400 F., a flash point of 113 F. and contained 100% aromatic hydrocarbons. Its blending aviation octane number was 105 and its rich performance number was 159. A greater yield of a fuel having even higher octane ratings could be obtained by taking a wider cut from the product, namely one boiling from 280 to 420 F. but with considerable loss in flash point. The methods employed for obtaining the various octane ratings are adequately described in the lituerature.

Inthe foregoing examples the catalyst em ployed was one in which the zinc aluminate base was prepared using zinc nitrate as starting material. It is also possible to prepare zinc aluminate from zinc sulfate as starting material but in this case certain precautions must be observed. One of the problems is that when the zinc aluminate is precipitated from a solution of zinc sulfate and a soluble aluminum compound, S04 radical is occluded in the precipitat and cannot be washed therefrom with water. The presence of sulfate in the zinc aluminate spinel is undesirable. For example, it has been found thatwhen the zinc aluminate spine] base contained 6.1 per cent S04 by weight and was employed to aromatize normal heptane under conventional testing conditions, 44 per cent aromatics, based on feed, was formed. On the other hand, when the same base, tested under identical conditions in aromatizing normal heptane, contained 12 per cent by weight S04, the yield of aromatics was only 31 per cent based on feed. While it is possible to reduce this sulfate content by washing with alkaline solutions or by treating the catalyst at elevated temperatures with hydrogen and steam, these procedures are less preferable than using direct methods of preparing catalysts having a low content of sulfate.

The methods outlined below for the preparation of zinc aluminate from zinc sulfate can also be applied to the preparation of this material from zinc chloride, since here also the problem of reducing the occlusion of anions without favoring the occlusion of sodium is encountered. Two methods of preparing the zinc aluminate spinel from zinc sulfate are as follows:

, Exam 12 Fourteen hundred sixteen grams of C. P. zinc sulfate and 105 cc. of concentrated sulfuric acid were dissolved in water to make 5049 cc. of solution A. Twelve hundred grams of sodium aluminate was stirred for 10 minutes in 6000 cc. of water. One liter of filter aid was added. the solution was filtered, and 5049 cc. of filtrate was taken as solution B. Five liters of water was stirred vigorously in a. 5-gallon crock while solutions A and B were added simultaneously and at the same rate over a 30-minute period. More water was added during the precipitation to facilitate stirring. After the final slurry had been stirred l0 of distilled water, filtered and washed with 8 liters of distilled water. The cake was made into a thick paste with distilled water and was mixed with a solution of 40.9 g. ammonium molybdate in a blend of 25 cc. concentrated ammonium hydroxide' plus 250 cc. of distilled water. This gave a composition of 90 .parts by weight of ZnAhOa,

and 10 parts by weight of Mom. The mixture was ball milled 3 hours, dried with stirring, calcined 3 hours at 1200 F. and pilled. It was tested as a catalyst and gave the following results:.

I Catalytic aromatization 1000" r.; 1.2 v.Iv./hr.; 1 hr. periods: 1 atm. pressure] Per H Cent Per Cent Vol. Per Con- Selectivity Gent Net- Gas Coke verto Aromatics Aromatics sion n-Heptane Feed. 44' 16. 5 6. 0 200-270 F. East Texas Naphtha Feed 53 10. 8 8. 7

Exmrnr: 13

of sodium aluminate was stirred for 15 minutes in 65 liters of water. About 6 liters of filter aid was stirred in and the mixture was filtered with a filter crock. Fifty-seven and three tenths liters of the filtrate was taken as solution B.

Twelve liters of water was poured into a 50- gallon barrel and stirred vigorously while solutions A and B were added simultaneously and at the same rate from calibrated bottles during a period of one hour.

The pH of the liquid portion of the slurry was found to be 12. Portions of sulfuric acid diluted 20 to 1 were added with stirring until the pH was reduced to 7.5 (Three hundred and fifty cc. of concentrated sulfuric acid diluted with 7 liters of water was added in all.)

The slurry was then pumped into a filter press containing ten plates, 1" by 18" by 18". At a pressure of 65 pounds per sq. inch only about seven-eights oi the slurry could be pumped into the press. The material in th press was washed with 60 gallons of water per hour for 3 hours. It was than air blown for 30 minutes and dumped. The cake was resuspended in water ins. 50 gallon barrel and left overnight. The next morning the slurry was again pumped into the ten-plate press. This time the press was not filled, indicating shrinkage of the precipitate. The press was washed with water at the rate of 150 gallons per hour for 3 /2 hours. It was then air blown for half an hour and dumped. v

The cake was worked into a very thick plaste by means of large propeller-type stirrers. The waterv added in this step was kept to a minimum. A solution of 1220 g. of C. P. ammonium molybdate dissolved in 9 liters of water was then stirred into the paste to form a thick slurry whichwas allowed to stand overnight. The slurry was then dried in an oven with air circulation at 240 to 400 1}. The wet material was stirred occasionally toinsure uniformity. The product was calcined 3 hours in an electric muille at 1200 F. and then pilled.

v Norn.--The pHs given above were determined with a commercially available. testing paper. Checks with a glass electrode pH meter have indicated that the paper values of 12 to 13 correspond'to glass electrode values of approximately 40 10.5 to 12 and a paper value of 7.5 gives an electrode value of 8.5.

When tested as a catalyst, the following results I In the preceding examples care was taken to maintain the pH of the solution from which the precipitate was formed at about 9, to 12. At the end of the precipitation the pH was adjusted to a value of within the range of from 7 to 8. By

. thus proceeding, namely, by limiting th pH during the precipitation within the range of from 9 to 12, the quantity of sulfate radical occluded in the precipitate is restricted to an amount not exceeding 5 percent by weight. At the same time, by adjusting the final pH of the filtrate to a value between 7 and 8. the sodium was desorbed in the final precipitate so that it did not exceed about one-tenth of 1 per cent and thus was assured the production of catalysts of reproducible activity.

In the two preceding. examples are disclosed methods of forming the zinc aiuminate spine! base in which two solutions were mixed, namely zinc sulfate containing sulfuric acid and sodium aiuminate containing sodium hydroxide. Instead of so proceeding, a solution containing zinc sulfate and aluminum sulfate may be mixed with an alkali such as sodium or ammonium hydroxide. It will be understood, however, that in these modifications the same precautions must be observed as regards-the pH of the supernatant liquid in the precipitating medium, including the maladjustment thereof.

Instead of using a commercial sodium aluminate, one may use an aluminumoxide, such as A12Oa.3H2O dissolved in an alkaline solution.

In any of the methods of preparing zinc aiuminate, whether from zinc sulfate, nitrate or other salt, it is to be understood that sodium carbonate may be used in place of sodium hydroxide as precipitating agent. Also, by conducting the precipitation at 60-100 C. rather than at room temperature, catalyst bases of lower density and increased pore size may be prepared.

As previously indicated. thezinc aiuminate composition prepared from zinc sulfate is more heat stable than the zinc aiuminate composition prepared from zinc nitrate as is shown by the following data:

Catalytic dramatization 1000 n; l.2v./v./hr. Catalyst composition: war/100.; 90% ZnAhOd This is important because in preparing the catalyst the material is calcined ordinarily in a kiln and the more heat stable catalyst does not require the critical control that the lss heat stable catalyst requires; and, furthermore, in the regeneration of the catalyst after use in hydroforming or aromatizing operations the more heat stable catalyst is less liable to injury during regeneration, an operation usually performed by burning off the contaminants formed on the catalyst during use in the on -stream operation.

Another advantage of the catalyst prepared from zinc sulfate is that of increased activity as set forth below in the following data:

,catmlutic dramatization [1000 F. 1.2 v./v./hr.; 1 hr. period. Catalyst: 107 M00: on

' znahommm znsool 907 n-Heptane Feed Run #1 Run #2 Vol. Per Cent Conversion 90. 1 Vol. Per Cent Selectivity 66 56 Vol Per Cent Net Aromatics. 61 51 Wt. Per (lent Gas l8. 9 18.!) Wt. Per Cent Coke 5. 4 5.1

East Texas Naphtha Feed Run #3 Run #4 Vol. Per Cent Conversion.. 88 91 Vol. Per Cent Selectivity 55 55 Vol. Per Cent N at Aromatics. 48 50 Wt. Per Cent Gas a 13.0 12.2 Wt. Per Cent Coke.-. 7. 0 7.8

These results are higher than ever obtained from the same type of catalysts tested under similar conditions but in which the catalyst base was zinc aluminate that had been prepared from zinc nitrate.

In the runs set forth in the two preceding tables, the pressure in the reaction zone was approximately 1 atmosphere and no added hydrogen was present in the reaction zone.

Instead of coprecipitating the zinc and the alumina, one may separately precipitate zinc hydroxide and aluminum hydroxide from any suitable source and thereafter mix the precipitates in suitable proportions to form the zinc aluminate. The mixture is then dried and finally calcined at above 800 F. and preferably at above 1000 F. Addition of molybdenum and/or chromium oxide may be successfully accomplished either before or after the drying process. For example, molybdenum oxide may be coprecipitated from a solution of an alkaline molybdate either at the same time the zinc aluminate is precipitated or at some later point in the preparation of the zinc aluminate.

Alternative methods of preparing zinc aluminate include: reaction of sodium zincate or of ammonium zincate with aluminum sulfate or nitrate; admixture of sodium aluminate and sodium or ammonium zincate and coprecipitation with sulfuric or nitric acid; and precipitation of admixed sodium aluminate and sodium or ammonium zincate with zinc and aluminum sulfates or nitrates. Still another method is to convert zinc and aluminum chloride into zinc and aluminum oxide gels by reaction with ethylene oxide.

Also, zinc and aluminum or their alloys may be converted to sols by action of dilute formic or acetic acid in the presence of mercury salts.

When using any of the methods given herein for the preparation of zinc aluminate it may be found advantageous to modify the gelatinous nature of the product by conducting the preparation in the presence of 1 to 10% (based on the dry catalyst) of an acetate, tartrate or citrate, e. g., ammonium acetate, or of 0.5% to 5% of a silicic acid sol or of glycerol, starch, vegetable gums and the like.

To review briefly, it has beenfound that when alumina is modified by reacting it with a zinc compound to form zinc aluminate the resulting product is more heat stable than aluminum oxide. Furthermore, the activity of molybdenum oxide and chromium oxide catalysts is greater when using zinc aluminate rather than alumina as the.

base or support. The improved base makes it possible to obtain good yields of aromatics by aromatization of paraifins and it also improves the hydroforming process, since it results in the formation of increased quantities of aromatics in the product which is a highly desirable result since these aromatics increase the octane'rating of the said product. A number of other heavy metal divalent oxides have been tried as substitutes for zinc oxide without securing any definite improvement in the alumina base.

This is illustrated in the table presented below. These data were obtained in aromatization tests conducted by the method employed in Example 4. All these tests were run at 1000 F. using a feed rate of 1.2 volumes of normal heptane per volume of catalyst per hour at about atmospheric pressure. The catalyst in each instance consisted of molybdenum oxide supported on the catalyst base indicated.

It will be seen that whereas zinc aluminate spinel was much better than alumina as a catalyst support all of the other metal aluminates were either no better than or were inferior to alumina.

Although from 5 to 30% of molybdenum oxide or of chromium oxide or of mixtures of these oxides may be employed in these catalyst compositions, from about 10% to about 20% of these oxides is particularly desirable. The effect of varying the molybdenum oxide content of the zinc aluminate-molybdenum oxide catalyst composition is shown in the following table of data obtained under aromatization conditions, that is, at atmospheric pressure and with no added hydrogen.

Efiect of M 00: content on catalyst activity [1000 F., 1.2 v./v./hr. feed rate, 1 hr. perioda] Percent ZnAlzOl 100 95 90 70 Percent M003 0 5 10 20 30 n-Heptane Vol. Percent I\et Aromatics 18 47 37 Wt. Percent Gas 13 13. 4 15. 2 l7. 1 l4. 7 Wt. Percent Coke 4. 5 4.1 5.1 4 7. l

200270 F. Naphtha Vol. Percent Net Aromatim 20 34 44 40 Wt. Percent Gas 6. 8 7.8 0. 2 9. 8 8.9 Wt. Percent Coke 5. 1 4. 2 6. 6 7. 7 7. 5

It is to be understood that although the present invention is concerned with improved reforming or aromatization reactions, the new catalysts disclosed herein may be used in a number of other reactions. For instance, they may be used in the dehydrogenation of parafllns to olefins or of olefins to diolefins, desulfurization of sour petroleum oils, oxidation reactions, destructive hydrogenation of petroleum oil, coal tar oil, coal, and the like.

Although it is preferable that the zinc aluminate catalyst base be prepared by combining aluminum oxide and zinc oxide in molecular proportions, slight excesses of either component are not harmful. Thus an excess of either reactant may be used in making the zinc spinel or one may admix a slight excess of either ZnO or A1203 with the zinc spinel. Furthermore, it has been found that addition of small percentages of promoters is sometimes beneficial, for example, 0.1 to 0.5% of Ni or Pt. Addition of 0.5 to 5% of calcium oxide to the catalyst compositions may be made when it is desired to improve the resistance of molybdenum oxide to oxidation and reduction.

These catalysts may be formed into pills, pel-' lets, orother shaped bodies either before or after the calcination and with or without the use of pilling aids, such as graphite, starch, solid hydrogenated-vegetable fat, etc. The pellets and other shaped bodies may also be formed by extrusion methods. One good method of forming the catalysts into desired shapes is to dry the precipitate in a high humidity atmosphere. For

example, a one-inch filter cake can in this waybe dried into granules, 90 per cent of which will have a particle size of 2 to 8 mesh. This method of forming the catalyst into desired shapes is important for the reason that it is much less expensive than when the catalyst is formed into pills using pilling machinery.

Of course, in the case where the processes of the present invention are conducted in what is known as a fluid" catalyst system, the catalyst may be ground either before or after calcination to a size range smaller than 500 microns, preferably within the range of 20 to 200 microns. The dried or calcined material from this grinding operation which is too fine to use may be mixed with wet catalyst in order to agglomerate it into a usable coarse size range.

It will be understood that these catalysts after use in aromatization or hydroforming operations, having become contaminated with carbonaceous deposits, may be regenerated by burning oil! these deposits by treatment with an oxygen-containing gas. This regeneration may be accomplished in a normal manner, conventional in the art except that these new catalysts are more heat stable than the ordinary hydroforming catalysts such as those oxides which are supported on an alumina base.

Numerous modifications of the invention falling within the scope thereof may be made by those familiar with this art.

What is claimed is:

1. A method of treating hydrocarbons which comprises contacting said hydrocarbons at elevated temperatures with a catalyst composition consisting of at least 70% of zinc aluminate spinel supporting at least one metal oxide selected from the group consisting of molybdenum oxide and chromium oxide.

' 2. Method according to claim 1 in which naphthenic hydrocarbons are converted to aromatic hydrocarbons.

3. Method according to claim 1 in which parafiinic hydrocarbons are converted to aromatic hydrocarbons.

4. Method according to claim 1 in which normal heptane is converted to toluene.

5. A method of converting normal heptane to toluene which comprises vaporizing the said heptane and contacting the vapors at elevated temperatures in a reaction zone with a catalyst consisting of about 90% zinc aluminate and about 10% molybdenum oxide for a sufficient period of time to effect the desired conversion, and recovering from the reaction zone a product containing substantial quantities of toluene.

6. A method for increasing the aromaticity of hydrocarbon mixtures which comprises contacting the hydrocarbon mixtures at elevated temperatures in a reaction zone with a catalyst composition consisting of at least 70% of zinc aluminate spinel supporting at least one metal oxide selected from the group consisting of molybdenum oxide and chromium oxide, for a sufficient period of time to effect the desired conversion, and recovering from the reaction zone a product con- 16' taining substantial quantities of .aromatic hydrocarbons.

7. A method of reforming a'petroleum naphtha fraction which comprises contacting the said fraction at elevated temperatures with a catalyst composition consisting of at least of zinc aluminate spinel supporting at least one metal oxide selected from the group consisting of molybdenum oxide and chromium oxide.

8.Method according to claim 7 conducted in the presence of added hydrogen.

9. Method according to claim 7 which is conducted at elevated pressures.

10. Method according to claim 7 in which the naphtha is contacted at temperatures of about 900 F. to 1000 F. with a catalyst composition consisting of from about to about90% of zinc alumin-ate spinel and from about 10% to about 20% of metal oxides selected from the class consisting of molybdenum oxide and chromium oxide. v

11. Method according to claim 7 in which the catalyst composition consists of about 90% zinc aluminate and about 10% of chromium oxide.

12. Method according to claim 7 in which the catalyst composition consists of about 90% zinc aluminate spinel and about 10% molybdenum oxide.

13. Method according to claim 7 in which the catalyst composition consists of about zinc aluminate, about 10% of molybdenum oxide and about 5% of chromium oxide.

14. The method of preparing a safety aviation fuel which comprises vaporizing a heavy virgin naphtha containing naphthenes and contacting the vaporized naphtha in a, reaction zone with a catalyst composition consisting of at least 70% of zinc aluminate spinel supporting at least one metal oxide selected from the group consisting of molybdenum oxide and chromium oxide, and in the presence of an added gas containing free hydrogen, permitting the naphtha to remain resident in the reaction zone for a sufficient period of time to effect the desired conversion, and thereafter recovering from the reaction zone a safety aviation fuel of high aromaticity and improved octane quality.

1.5. The method set forth in claim 14 in which the temperature in the reaction zone is from about 900 F. to 1000 F. and in which a pressure of from atmospheric'to200 lbs. per sq. in. is maintained.

16. Method as set forth in claim 14 in which the catalyst composition consists of about zinc aluminate and about 10% molybdenum oxide.

KENNETH K. KEARBY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENT Number Name Date 1,732,381 Schmidt et al. Oct. 22, 1929 2,344,330 Sturgeon Mar. 14, 1944 2,367,530 

